The present invention relates generally to detection of an arc condition.
As is known, integrated electronic circuits or xe2x80x9cchipsxe2x80x9d are manufactured as dice on a semiconductor wafer. After manufacture of a wafer, each die on the wafer is subjected to functionality tests to identify defective dice and/or to rate properly functioning dice.
FIG. 1 illustrates a common system for testing semiconductor wafers. A prober 124 includes a boat 120 for storing wafers. A robotic arm 122 moves the wafers between the boat 120 and a stage 118. Once a wafer 116 is placed on the stage 118, the stage is moved such that dice on the wafer contact probes 114 on a probe card assembly 112. Numerous electrical connections 110 connect the probe card assembly 112 to a test head 108. A tester 102 controls testing of a wafer 116. Communication cables 104 and 106 connect the tester 102 to the test head 108 and the prober 124.
The tester 102 controls testing of a wafer 116 by sending commands to the prober 124 and commands and test data to the test head 108 via communication cables 104 and 106. The tester 102 also receives status from the prober 124 and status and response data generated from the test head 108 also via communication cables 104 and 106.
To test wafers, the tester 102, which is typically a computer, executes a test program designed specifically for the wafers. A typical test program begins by sending commands to the prober 124 to remove a wafer from the boat 120 and place the wafer on the stage 118. The test program then sends commands to the prober 124 causing the stage 118 to move the wafer 116 into contact with the probes 114 of the probe assembly 112. The test program then sends test data to the test head 108. The test data is input to dice on the wafer 116 via the probe assembly 112. Response data generated by the dice on the wafer 116 is output from the dice through the probe card assembly 112 to the test head 108, from where it is sent to the tester 102. The tester 102 then evaluates the test data, determining whether the tested dice are functional or defective and sometimes rating the tested dice.
Because a typical probe assembly 112 does not have enough probes 114 to contact all of the dice on a wafer 116, the stage 118 must repeatedly move the wafer with respect to the probe elements. Thus, once the dice on wafer 116 in contact with probes 114 are tested, the tester 102 issues commands to the prober, causing the stage 118 to reposition the wafer 116 so that the probes 114 contact other as yet untested dice on the wafer.
Among the signals communicated to the dice on wafer 116 via probes 114 are power signals to provide power to the dice. If, however, power is applied to any of probes 114 as the wafer 116 is being moved either into contact with the probes or out of contact with the probes, an arc of electricity may jump the gap between the probes and the contact pads on the dice. Such an arc can damage the probes, the contact pads on the dice, or both. Although arcing is most likely to occur where probes 114 are delivering power to the dice, arcing may also occur where probes are delivering data or other types of signals to the dice. It is thus important that the test program executed by the tester 102 cause the test head 108 to power down at least those probes 114 that are delivering power to the dice while the stage 118 is moving the wafer 116. It may also be helpful to power down all probes 114 while the stage 118 is moving the wafer 116.
While probes in a semiconductor test system are being moved into or out of contact with a semiconductor wafer, the voltage level of power supplied to selected ones of the probes is monitored. If the voltage level of the power exceeds a level that could cause an arc between the probes and the semiconductor wafer while the wafer is being moved, an indication is generated that an arc condition has been detected.